There is nothing more frustrating when finishing a large electronics project then finding out that your project doesn’t work as intended. The causes for this can vary wildly, but a bad solder joint is one of the more common reasons for circuitry failure. As such, you should follow these steps to verify that each new solder joint is good before continuing with your project.
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It may sound like common sense, but visually inspecting the solder joint should be your first step. Inspect the joint with a magnifying glass and move or wiggle the component to check for stability. Remove and re-solder components that feel loose. Also verify that the pad is filled with solder, but not overfilled. The pad and the lead should be completely covered with solder and you shouldn’t be able to see through the hole the lead passes through.
Also check for Shiny solder, which indicates that the solder was melted and re-cooled properly. Generally solder that didn’t reach a hot enough melting temperature will appear cloudy when re-cooled. This tip doesn’t apply to all solder, however, so take it with a grain of salt. (Some of the newer lead-free solder will always appear cloudy).
Last, make sure that the cooled solder isn’t touching another pad, which will create a short and cause your circuit to not operate as expected.
Set the dial on your multimeter to the Ohm function. Sometimes it will be labeled “Ohm x 1K”. The icon for Ohms looks like an upside down U or a set of headphones.
Touch the leads of your multimeter together before beginning. You should get a zero reading, indicating there is zero resistance between the leads currently.
Now, touch the positive lead of your multimeter to some part of the wire ahead of the solder joint. Then touch the negitive lead to the end of the post of the connector on the other side of the solder joint. Your meter should read zero. If you see any kind of resistance, it likely reflects a bad solder joint.
You can also use the continuity function on your multimeter to test a solder joint. First, set your multimeter to continuity mode (looks like sound waves going out left to right in a cone shape). Touch the leads together and make sure the multimeter beeps.
Now, touch the leads to two points on opposite sides of your solder joint. The multimeter will beep if there is continuity detected. This means that conductive material (i.e. your solder joint) is connecting the points between your leads and that the solder joint is good from a continuity standpoint. If the multimeter does not beep, you do not have continuity.